Delete Azure AD

I had created an AD directory named alextestad in my Azure subscription in order to do some experiments, after that i tried to delete this temp AD, but i received
After some struggle i found how to do.
First must be added an Global admin user to this AD, in my case I added a user named “tobedeleted”

This causes the request of login where we use the credentials of the new user:
and then

connect-msolservice -credential $objCred

done this , we can launch in Powershell

Get-MsolServicePrincipal | Select DisplayName

This instructions lists all the applications Service Principals in AD, in my case
Now we can delete all not required apps in AD tenant

Get-MsolServicePrincipal | Remove-MsolServicePrincipal

where I got some errors but it seems no problem
Reissuing Get-MsolServicePrincipal | Select DisplayName in my case we had
Now in Azure portal is needed to delete the temp user, with the DELETE button at the end of this page
Done this, finally no errors while trying to delete the AD: